Answered by Shaykh Faraz Rabbani
Can one sleep right after praying fajr? maghrib? asr? I can not seem to get myself up for tahajjud so if I was to pray the tahajjud namaz right after isha is that possible?
Fajr: it is permitted to sleep after it, though it is best not to sleep until after sunrise. This is a time where dhikr and Qur’anic recitation is of great reward. The Messenger of Allah (upon him be the best of blessings and most perfect of peace) said that the one who sits from after the fajr prayer until sunrise in the remembrance of Allah shall have the complete reward of a hajj and umrah…
Asr: It is allowed to sleep after it, though it is better (if possible) to sleep after Zuhr.
Maghrib: It is best not to sleep until having prayed Isha, unless you are sure that you will wake up for Isha. Tahajjud prayer is prayer performed after sleep at night. One should take the means to get up for tahajjud, because of the great reward mentioned regarding it in the Qur’an and Prophetic teachings. If you don’t think you can get up one night because of an excuse such as travel, sickness, or the like, then you should pray what you normally pray for tahajjud before sleep. In general, nafl prayers at night (even before sleep) have more reward than nafl prayers during the day.